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Add a delay to tearing down threads.

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It's been observed that in certain workloads (zvol-related being a
big one), ZFS will end up spending a large amount of time spinning
up taskqs only to tear them down again almost immediately, then
spin them up again...

I noticed this when I looked at what my mostly-idle system was doing
and wondered how on earth taskq creation/destroy was a bunch of time...

So I added a configurable delay to avoid it tearing down tasks the
first time it notices them idle, and the total number of threads at
steady state went up, but the amount of time being burned just
tearing down/turning up new ones almost vanished.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #14938
This commit is contained in:
Rich Ercolani
2023-06-26 16:57:12 -04:00
committed by GitHub
parent 8e8acabdca
commit 35a6247c5f
3 changed files with 49 additions and 1 deletions
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module/os/linux/spl/spl-taskq.c
+33 -1
View File
@@ -36,6 +36,12 @@ static int spl_taskq_thread_bind = 0;
module_param(spl_taskq_thread_bind, int, 0644);
MODULE_PARM_DESC(spl_taskq_thread_bind, "Bind taskq thread to CPU by default");
static uint_t spl_taskq_thread_timeout_ms = 10000;
/* BEGIN CSTYLED */
module_param(spl_taskq_thread_timeout_ms, uint, 0644);
/* END CSTYLED */
MODULE_PARM_DESC(spl_taskq_thread_timeout_ms,
"Time to require a dynamic thread be idle before it gets cleaned up");
static int spl_taskq_thread_dynamic = 1;
module_param(spl_taskq_thread_dynamic, int, 0444);
@@ -848,12 +854,37 @@ taskq_thread_should_stop(taskq_t *tq, taskq_thread_t *tqt)
tqt_thread_list) == tqt)
return (0);
return
int no_work =
((tq->tq_nspawn == 0) && /* No threads are being spawned */
(tq->tq_nactive == 0) && /* No threads are handling tasks */
(tq->tq_nthreads > 1) && /* More than 1 thread is running */
(!taskq_next_ent(tq)) && /* There are no pending tasks */
(spl_taskq_thread_dynamic)); /* Dynamic taskqs are allowed */
/*
* If we would have said stop before, let's instead wait a bit, maybe
* we'll see more work come our way soon...
*/
if (no_work) {
/* if it's 0, we want the old behavior. */
/* if the taskq is being torn down, we also want to go away. */
if (spl_taskq_thread_timeout_ms == 0 ||
!(tq->tq_flags & TASKQ_ACTIVE))
return (1);
unsigned long lasttime = tq->lastshouldstop;
if (lasttime > 0) {
if (time_after(jiffies, lasttime +
msecs_to_jiffies(spl_taskq_thread_timeout_ms)))
return (1);
else
return (0);
} else {
tq->lastshouldstop = jiffies;
}
} else {
tq->lastshouldstop = 0;
}
return (0);
}
static int
@@ -1091,6 +1122,7 @@ taskq_create(const char *name, int threads_arg, pri_t pri,
tq->tq_flags = (flags | TASKQ_ACTIVE);
tq->tq_next_id = TASKQID_INITIAL;
tq->tq_lowest_id = TASKQID_INITIAL;
tq->lastshouldstop = 0;
INIT_LIST_HEAD(&tq->tq_free_list);
INIT_LIST_HEAD(&tq->tq_pend_list);
INIT_LIST_HEAD(&tq->tq_prio_list);